Video display device and color temperature correction method for the same

BACKGROUND OF THE INVENTION

0001The present invention relates to a method for correcting the color temperature of the picture signals and a picture display device of such as a color television receiver and a liquid crystal projector.

0002In such display devices as mentioned above, it is generally known that an especially bright white color is rendered bluish to some extent for display thereon by increasing the color temperature thereof so as to make the pictures visually impressive and beautiful.

0003It is disclosed in the Japanese Unexamined Patent Publication 23414/1995 that portions in such achromatic colors as white and gray are detected based on the maximum values of three types of color difference signals R-Y, G-Y and B-Y in order to enhance the level of the B-Y so as to strengthen the blue component of such portions and increase the color temperature thereof.

SUMMARY OF THE INVENTION

0004However, the actual pictures include besides a pure white color a color approximate to white, which color is made with a slight mixture of other colors with the pure white color and is hereinafter referred to as approximate white color and also as white attributes together with the pure white color. It often happens that what is seen in white in such natural pictures as scenery and portraits is in actual mostly occupied by the approximate white rather than the pure white color. In the prior art as mentioned above, it is arranged such that only the color temperature of such portions in achromatic colors is increased so that color temperature correction is performed only on the region in pure white of the natural pictures, most of which composition is occupied by such approximate white as mentioned above. Accordingly, visual effect is not brought by the rise of the color temperature of such portions to much extent, when the pictures are seen as a whole.

0005Further, there is a case where it appears more beautiful when the approximate white or slight yellow attribute to the pure white color that is of low color temperature is altered with bluish attribute to the pure white color that is of high color temperature. Moreover, where the display device provided with such color reproduction characteristics as displaying the portions of a picture in white attributes by a lower color temperature than the color temperature of the relevant video signals, such as displaying the pure white color in yellowish attribute thereto, it is visually preferable to increase the color temperature of not only the pure white color, but also that of the approximate white color, the color temperature of which is low. However, the above prior art is not so arranged as increasing the color temperature of the approximate white color, which does not meet such requirement as mentioned above.

0006In view of the above inconveniences as encountered with the prior art, the present invention is to provide a video display device that more appropriately corrects the color temperature of the pictures so as to display them in more preferred colors and a color temperature correction method for the same.

0007The video display device according to the present invention is characterized in being provided with a signal processing circuit provided with a color temperature correction circuit that corrects the color temperature of the input video signals of the white attributes including the approximate white color having a given luminance or above and a given chroma saturation or below

0008Concretely, the signal processing circuit comprises an A/D converter that converts an input video signal into a digital signal, a matrix circuit that converts the digital signal as output from the A/D converter into a luminance signal and at least two color difference signals, a hue processing circuit to obtain a hue signal on the basis of the color difference signal as output from the matrix circuit, a chroma saturation processing circuit to obtain a chroma saturation signal on the basis of the color difference signal and a microcomputer, wherein the color temperature correction circuit is characterized in performing color temperature correction processing for the purpose of increasing the color temperature of the hue signal as output from the hue processing circuit and the chroma saturation signal as output from the chroma saturation circuit, which signals belong to the white attributes, or for the purpose of approximating the color temperature of the white attributes to that of blue color.

0009The color temperature correction circuit comprises a first color temperature correction section that performs the color temperature correction on the hue signal as output from the hue processing circuit, which signal belongs to the white attributes, a second color temperature correction section that performs the color temperature correction on the chroma saturation signal as output from the chroma saturation processing circuit, which signal belongs to the white attributes, a first selection circuit that selects and outputs either a signal as output from the first color temperature correction section or a hue signal as output from the hue processing circuit and a second selection circuit that selects and outputs either a signal as output from the second color temperature correction section or the hue signal as output from the hue processing circuit. Further, the first and second selection circuits are arranged such that they select the signals as output from the first and second color temperature correction sections where the region of the input video signal, which region belongs to the white attributes and has a given luminance or above and a given chroma saturation or below, is detected.

0010Further, the color temperature correction method according to the present invention is characterized in comprising a step of converting an input video signal into a digital signal, a step of separating the digital signal into a luminance signal and a color difference signal, a step of separating the color difference signal into a hue signal and a chroma saturation signal and a step of performing color temperature correction processing on the hue and the chroma saturation signals, which signals belong to the white attributes and have a given luminance or above and a given chroma saturation or below, so as to increase the color temperature of the same signals. The step of performing the color temperature correction processing may further include a step of approximating the hue of the signals belonging to the white attributes to blue color and a step of increasing the chroma saturation of the signals belonging thereto.

0011The present invention is arranged such that the color temperature correction is performed on the signal, which signal belongs to the white attributes and has a given luminance or above and a given chroma saturation or below, which allows the color temperature of the signal not only in pure white, but also in the approximate white color with the slight mixture of other colors to be corrected. Thus, even though pictures like natural scenery and portraits include a lot of approximately white portions, correcting the color temperature of such approximate white color so as to increase or approximate the same color to blue allows a visually preferred white color to be obtained, with the result that more beautiful video pictures can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

0012<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram to show one embodiment of the signal processing circuit for the video display device according to the present invention.

0013<figref idref="DRAWINGS">FIG. 2</figref> is a view to show a hue circle that denotes colors in vector.

0014<figref idref="DRAWINGS">FIG. 3</figref> is a view to show one example of the correlation between a hue signal and a chroma saturation signal.

0015<figref idref="DRAWINGS">FIG. 4</figref> is a view to show the input and output characteristics of the respective sections of the hue correction circuit <b>20</b>.

0016<figref idref="DRAWINGS">FIG. 5</figref> is a view to show the input and output characteristics of the respective sections of the hue correction circuit <b>20</b>.

0017<figref idref="DRAWINGS">FIG. 6</figref> is a view to show the range of the signals belonging to the white attributes as detected by the detection circuit <b>17</b>.

0018<figref idref="DRAWINGS">FIG. 7</figref> is a block diagram to show the details of the first color temperature correction section <b>231</b>.

0019<figref idref="DRAWINGS">FIG. 8</figref> is a view to show the operation of the first color temperature correction section <b>231</b>.

0020<figref idref="DRAWINGS">FIG. 9</figref> is a view to show the input and output characteristics of the respective sections of the first color temperature correction section <b>231</b>.

0021<figref idref="DRAWINGS">FIG. 10</figref> is a view to show the input and output characteristics of the second and third hue shift coefficient generation circuits <b>2341</b> and <b>2342</b>.

0022<figref idref="DRAWINGS">FIG. 11</figref> is a block diagram to show the details of the second color temperature correction section <b>235</b>.

0023<figref idref="DRAWINGS">FIG. 12</figref> is a view to show the input and output characteristics of the respective sections of the second color temperature correction section <b>235</b>.

0024<figref idref="DRAWINGS">FIG. 13</figref> is a view to show the input and output characteristics of the respective sections of the chroma saturation correction circuit <b>22</b>.

0025<figref idref="DRAWINGS">FIG. 14</figref> is a block diagram to show another embodiment of the present invention.

0026<figref idref="DRAWINGS">FIG. 15</figref> is a view to show the range of the signals belonging to the white attributes as detected by the detection circuit <b>17</b>′.

0027<figref idref="DRAWINGS">FIG. 16</figref> is a block diagram to show another embodiment of the present invention.

0028<figref idref="DRAWINGS">FIG. 17</figref> is a block diagram to show the details of the luminance correction circuit <b>151</b>.

0029<figref idref="DRAWINGS">FIG. 18</figref> is a view to show the input and output characteristics of the respective sections of the luminance correction circuit <b>151</b>.

BEST MODE FOR CARRYING OUT THE INVENTION

0030Hereinafter, the preferred embodiments of the present invention are described below with reference to the accompanying drawings. <figref idref="DRAWINGS">FIG. 1</figref> is a block diagram to show one embodiment of the signal processing circuit for the video display device according to the present invention. The R, G and B primary colors signals, which are input to an R terminal <b>11</b>, a G terminal <b>12</b> and a B terminal <b>13</b> respectively, are supplied to an A/D conversion circuit <b>14</b> so as to be converted into digital signals. A matrix conversion circuit <b>15</b> subjects the three primary colors signals (R, G, B) in digital form as output from the A/D conversion circuit <b>14</b> to matrix conversion processing so as to convert the same signals into a luminance signal Y as well as color difference signals (R-Y) and (B-Y), which luminance signal Y is output to a detection circuit <b>17</b> and an inverse matrix conversion circuit <b>27</b> respectively and which color difference signals (R-Y) and (B-Y) are output to a hue conversion circuit <b>18</b> and a chroma saturation conversion circuit <b>21</b> respectively. The hue conversion circuit <b>18</b> performs an attribute conversion operation as shown in the following equation 1, for instance, with the input (R-Y) and (B-Y) signals in use so as to output a hue signal (è) in digital form. <br /><i>è</i>=tan⁻¹{(<i>R</i>-<i>Y</i>)/(<i>B</i>-<i>Y</i>)}  (Equation 1)

0031On the other hand, the chroma saturation circuit <b>21</b> performs an attribute conversion operation as shown in the following equation 2, for instance, with the input (R-Y) and (B-Y) signals in use so as to output a chroma saturation signal (S) in digital form. <br /><i>S</i>=√{square root over ((<i>R</i>-<i>Y</i>)²+(<i>B</i>-<i>Y</i>)²)}{square root over ((<i>R</i>-<i>Y</i>)²+(<i>B</i>-<i>Y</i>)²)}  (Equation 2)

0032Hereafter, the hue and chroma saturation signals are described. As shown in <figref idref="DRAWINGS">FIG. 2</figref>, when the (B-Y) signal is taken on the horizontal axis while the (R-Y) signal is taken on the vertical axis, colors are represented with vectors. The direction of the respective vectors or an angle that the horizontal axis (B-Y) makes with the respective vectors indicates a hue (è) and the largeness of the respective vectors indicates chroma saturation (S). What colors are represented with vectors is called a hue circle, which is generally known. In this hue circle, for instance, magenta is represented with a vector locating by 45° apart from the (B-Y) axis as shown in FIG. <b>2</b>. That is, the hue (è) of the magenta is at 45°. The chroma saturation (S) is determined by the largeness of the respective vectors wherein the larger the vector is, the denser it is while the smaller it is, the dimmer it is. If the largeness of a vector is null, it shows that there is no color in issue. The hue of red, yellow, green, cyan, blue respectively is at 113.2°, 173.0°, 225.0°, 293.2° and 353.0°. The hue conversion circuit <b>18</b> outputs a hue signal in digital form wherein the same circuit outputs the range of hue from 0° to 359.9° as the digital signals ranging from 0 to 1023, given that the digital signal is in 10 bits precision. That is, this bit precision divides the hue of 360° by 1024 that is equivalent to 2 to the tenth power. The LLSB of the hue digital signal amounts to approximately 0.35°.

0033<figref idref="DRAWINGS">FIG. 3</figref> is a view to supplement what is described above, in which one example of the correlation between the hue signal and the chroma saturation signal is shown by a waveform <b>301</b>. <figref idref="DRAWINGS">FIG. 3</figref> takes the hue signal è (in 10 bits precision) on the horizontal axis thereof while taking the chroma saturation signal S (8 bits in precision) on the vertical axis thereof. The representative hues (B-Y), (R-Y), −(B-Y) and −(R-Y) are shown therein as 0, 256, 512 and 768 respectively.

0034On the other hand, the chroma saturation circuit <b>21</b> outputs the chroma saturation signals that indicate the largeness of the vectors corresponding to the hue signals ranging from 0 to 1023 as the corresponding digital signals. Given that this chroma saturation signals in digital form are in 8 bits precision, the chroma saturation circuit <b>21</b> outputs the corresponding digital signals ranging from 0 to 255.

0035The digitalized hue signals as output from the hue conversion circuit <b>18</b> are input to a hue correction circuit <b>20</b>, which circuit is provided with a local hue correction circuit <b>203</b> as well as adders <b>201</b> and <b>202</b> so as to correct and output the digitalized hue signals as input within the specific range of hue. The range of hue as corrected and the degree of correction as effected by the hue correction circuit <b>20</b> are determined by the variety of the set values as output from a microcomputer <b>40</b>. Then, the digitalized chroma saturation signals as output from the chroma saturation circuit <b>21</b> are input to a chroma saturation correction circuit <b>22</b>, which circuit is provided with a chroma saturation coefficient generation circuit <b>222</b> as well as a multiplier <b>221</b> and an adder <b>223</b> so as to correct and output the digitalized chroma saturation signals as input within the specific range of chroma saturation. The range of chroma saturation as corrected and the degree of correction as effected by the chroma saturation circuit are determined by the variety of the set values as output from the microcomputer <b>40</b>.

0036The digitalized hue signals as corrected (hereinafter, referred to as corrected hue signals) by the hue correction circuit <b>20</b> and the digitalized chroma saturation signals as corrected (hereinafter, referred to as corrected chroma saturation signals) are input to a color temperature correction circuit <b>23</b>, which circuit is the characteristic portion of the present invention and is arranged such that color temperature correction is performed on the corrected hue and chroma saturation signals in the white attributes having a given luminance or above and a given chroma saturation or below as defined by the maximum set value of chroma saturation ST and the minimum set value of luminance YB that are supplied from the microcomputer <b>40</b>. Further, the color temperature correction circuit <b>23</b> is provided with a first color temperature correction section <b>231</b> that performs color temperature correction on the corrected hue signal, a first selection circuit <b>232</b> that selects and outputs either a signal as output from the first color temperature correction circuit <b>231</b> or the corrected hue signal as output from the hue correction circuit <b>20</b>, a second color temperature correction section <b>235</b> that performs color temperature correction on the corrected chroma saturation signal and a second selection circuit <b>236</b> that selects either a signal as output from the second color temperature correction section <b>235</b> or the corrected chroma saturation signal as output from the chroma saturation circuit <b>22</b>. The first and second selection circuits <b>232</b> and <b>236</b> select and output the signals as output from the first color correction section <b>231</b> and the second color correction section <b>235</b> respectively where the input video signals are of a given luminance or above and a given chroma saturation or below while otherwise selecting and outputting the corrected hue and chroma saturation signals respectively. The selection operation of the signals as mentioned above by means of the first and second selection circuits <b>232</b> and <b>236</b> is performed on the basis of the control signals as output by a detection circuit <b>17</b>.

0037The detection circuit <b>17</b> detects whether the input vide signals are those in the white attributes having a given luminance or above and a given chroma saturation or below. Concretely, the detection circuit <b>17</b> comprises a luminance comparison circuit <b>171</b> that compares a luminance signal as output from a matrix conversion circuit <b>15</b> with the minimum value of luminance YB as set by the microcomputer <b>40</b>, a chroma saturation comparison circuit <b>172</b> that compares the corrected chroma saturation signal with the maximum value of chroma saturation ST as set by the microcomputer and a switching control circuit <b>173</b> to which the signals as output from the luminance comparison circuit <b>171</b> and the chroma saturation comparison circuit <b>172</b> are input, on the basis of which signals the switching control circuit determines whether the input video signals meet the condition that they are of a given luminance or above and a given chroma saturation or below so as to output the control signals to the first and second selection circuits <b>232</b> and <b>236</b> where such condition is met. That is, where such condition as mentioned above is met, the switching control circuit <b>173</b> is arranged such that the first and second selection circuits <b>232</b> and <b>236</b> select and output the signals as output from the first and second color correction sections <b>231</b> and <b>235</b> respectively.

0038The signals as output from the first and second selection circuits <b>232</b> and <b>236</b> are input to a color difference conversion circuit <b>26</b>, which circuit generates the color difference signals (R-Y) and (B-Y) from those output signals and outputs them. The color difference signals as output from the color difference conversion circuit <b>26</b> are input to an inverse matrix conversion circuit <b>27</b> so as to be converted into three primary colors signals of R, G and B. The three primary colors signals as output from the inverse matrix conversion circuit <b>27</b> are supplied to a display device <b>28</b>, which device displays video pictures on the basis of those three primary colors.

0039Then, the respective sections of the device are in more details described below. Firstly, the hue correction circuit <b>20</b> is described in details with reference to <figref idref="DRAWINGS">FIGS. 4 and 5</figref>. The hue correction circuit, where there is no addition to the digitalized hue signal at the adders <b>201</b> and <b>202</b>, is possessed with the linear input and output characteristics as shown in the straight line <b>401</b> of FIG. <b>4</b>A. The digitalized hue signal as output from the hue conversion circuit <b>18</b> is input to the adder <b>201</b> and the local hue correction circuit <b>203</b> respectively. The local hue correction circuit <b>203</b>, to which a mean value HP of hue, a level H thereof and a width W thereof as shown in <figref idref="DRAWINGS">FIG. 4B</figref> as output from the microcomputer <b>40</b> are input, decodes hue within the range of such input data so as to output a signal having a waveform as shown in <b>402</b> of FIG. <b>4</b>B. The adder <b>201</b> adds the digitalized hue signal to the signal as output from the local hue correction circuit <b>203</b> having such trapezoidal waveform <b>402</b>. As the result of it, the adder <b>201</b> outputs a signal having a waveform <b>501</b> that shifts by H upwards in the interval W with the middle HP thereof as shown in FIG. <b>5</b>A. The degree to which the waveform shifts depends on the level H as input from the microcomputer <b>40</b>. In this way, the local hue correction circuit <b>203</b> and the adder <b>201</b> variably control hue within the range as designated by the microcomputer <b>40</b> and with a level as designated by the same so as to allow hue to be locally controlled.

0040Further, the signal having the waveform <b>501</b> as output from the adder <b>201</b> is input to one terminal of the adder <b>202</b>. To the other terminal of the adder <b>202</b>, an offset value as output from the microcomputer <b>40</b> is input. This offset value is possessed with a given level a over the whole hue as shown in the straight line <b>502</b> of FIG. <b>5</b>B. The adder <b>202</b> adds the signal as output from the adder <b>201</b> to the offset value as output from the microcomputer <b>40</b>, which results that the adder <b>202</b> outputs a signal that shifts upwards the whole signal as shown in <figref idref="DRAWINGS">FIG. 5A</figref> by the level a of the offset value as shown in <figref idref="DRAWINGS">FIG. 5C</figref> with a waveform <b>503</b>. In this way, the adder <b>202</b> allows the overall hue to be controlled, the function of which corresponds to a so-called tint adjustment for the purpose of adjusting the overall hue. To note, the adder <b>202</b> according to the present embodiment adopts a 10 bits adder for both input and output operations so that it overflows and returns to 0 when the addition result goes beyond 1023. Accordingly, where the addition by means of the adder <b>202</b> results in being over 1023, it outputs a value that subtracts 1023 from the addition result.

0041As mentioned above, the hue correction circuit <b>20</b> varies the hue signal within the range of hue as designated by the microcomputer <b>40</b> with that of another hue and outputs a signal that offsets the whole hue by a given value by setting such offset value. The use of the 10 bits digital signal for the hue signal allows s high-precision hue shift and offset control as per approximately 0.350 to be realized. Such parameters relating to the hue correction as the degree to which and the range within which the hue shifts are set by the microcomputer <b>40</b>, which parameters are arbitrarily altered and adjusted. To note, there is only one range within which hue shifts according to the present embodiment, but the plurality of the local hue correction circuits <b>203</b> may be provided, the signals as output from which circuits are added so as to be input the adder <b>201</b>, which allows the plural ranges of hue to be shifted independently from one another.

0042Then, the chroma saturation circuit <b>22</b> is described below in details with reference to FIG. <b>13</b>. The chroma saturation circuit <b>22</b>, where there is neither addition to the digitalized chroma saturation signal at an adder <b>223</b> nor multiplication performed thereon at a multiplier <b>221</b>, is possessed with the linear input and output characteristics as shown in <figref idref="DRAWINGS">FIG. 13A</figref> with a straight line <b>1201</b>A. The digitalized chroma saturation signal as output from the chroma saturation circuit <b>21</b> is input to the multiplier <b>221</b> of the chroma saturation correction circuit <b>22</b>. On the other hand, the digitalized hue signal as output from the hue conversion circuit <b>18</b> is input to a local chroma saturation correction circuit <b>222</b>, to which circuit a mean value HP of hue, a level H thereof and a width W thereof as designated by the microcomputer <b>40</b> and as shown in <figref idref="DRAWINGS">FIG. 13B</figref> are input and which circuit decodes hue within the range of the input data so as to output a correction signal for locally correcting the chroma saturation of the hue of the specific range, which signal is shown in <figref idref="DRAWINGS">FIG. 13B</figref> with a waveform <b>1202</b>A. An adder <b>223</b> adds an offset value as output from the microcomputer <b>40</b> to a signal as output from the local chroma saturation signal correction circuit <b>222</b>. As the result of it, the adder <b>223</b> outputs a chroma saturation amplification coefficient with the characteristics as shown in <figref idref="DRAWINGS">FIG. 13C</figref> with a waveform <b>1203</b>A. Accordingly, it is the level H that determines the amplification degree of the chroma saturation signal within the specific range of hue while it is the offset value as designated by the microcomputer <b>40</b> that determines the amplification degree of the overall chroma saturation signals (or chroma saturation signals over the whole hue). This offset value is constant over the whole hue, the level of which value is set at 128 that is in the middle between the minimum value (0) and the maximum value (255) of the chroma saturation signals in the present embodiment. The signal as output from the adder <b>223</b> (chroma saturation amplification coefficient) is input to one terminal of the multiplier <b>221</b>, to the other terminal of which the digitalized chroma saturation signal as output from the chroma saturation conversion circuit <b>21</b> is input. The multiplier <b>221</b>, which multiplies the digitalized chroma saturation signal by the chroma saturation amplification coefficient, shifts or corrects the chroma saturation level within the specific range of hue.

0043In this way, the chroma saturation correction circuit <b>22</b> locally corrects the chroma saturation signal within the range of hue as designated so as to vary the density of the color within the specific range of hue, which circuit also controls the chroma saturation signals of the whole hue so as to vary the density of the color over the whole hue. This function corresponds to a so-called color adjustment. Further, such parameters relating to chroma saturation correction as the degree to which and the range within which the chroma saturation is corrected are designated by the microcomputer <b>40</b>, which allows those parameters to be altered and adjusted. To note, there is only one range for chroma saturation correction in the present embodiment, but the plural local chroma saturation circuits may be provided, the signals as output from which circuits are added so as to be input to the multiplier <b>221</b>, which allows the chroma saturation within the plural ranges of hue to be independently corrected.

0044Then, the detection circuit <b>17</b> is described below in details with reference to FIG. <b>6</b>. The luminance signal Y as output from the matrix conversion circuit <b>15</b> is input to a luminance level comparison circuit <b>171</b>, which circuit compares the luminance signal Y with the minimum set value of luminance YB (<b>601</b>) as shown in <figref idref="DRAWINGS">FIG. 6</figref> so as to output a high luminance level detection signal ‘1’ where the luminance signal Y is larger than the set value YB while to output ‘0’ otherwise. The minimum set value of luminance YB is defined as <b>210</b> in the present embodiment, which corresponds to the 70% of the maximum luminance <b>100</b>. That is, the present embodiment is intended for detecting the signals in the white attributes having 70% or more of luminance, to which value it is not necessarily limited, but may adopt other value where appropriate.

0045In turn, the chroma saturation signal as output from the multiplier <b>221</b> of the chroma saturation circuit <b>22</b> is input to a chroma saturation level comparison circuit <b>172</b>, which circuit compares the chroma saturation signal with the maximum set value of chroma saturation ST (<b>602</b>) as shown in <figref idref="DRAWINGS">FIG. 6</figref> so as to output a low chroma saturation level detection signal ‘1’ where the chroma saturation signal is smaller than the set value ST while to output ‘0’ otherwise. The maximum set value of chroma saturation ST is defined as 10 in the present embodiment, which value corresponds to the color temperature of 4000K (Kelvin) for the signals in yellowish white. That is, the present embodiment is intended for detecting the signals in the white attributes, the color temperature of which signals is 4000K or more, to which value it is not necessarily limited, but may adopt other value in an arbitrary manner. Further, the same set value of the color temperature may be applied to the whole hue whereas the different set value thereof may be applied to the specific range of hue. For instance, the set value of the color temperature for the signals in bluish white may be 20000K.

0046Both the high luminance level detection signal and the low chroma saturation level detection signal are input to the switching control circuit <b>173</b>, which circuit performs an AND operation on those detection signals so as to determine whether the input video signals are those in the white attributes having a given luminance or above and a given chroma saturation or below, in other words, those in very bright and very dim white. In short, the switching control circuit <b>173</b> discerns whether the input video signals exist within a cylindrical area drawn with the slanting lines as shown in <figref idref="DRAWINGS">FIG. 6</figref>, which area belongs to the signals in the white attributes, and outputs a flag signal ‘1’ when the input video signal is within the same area, which means that those two detection signals amount to ‘1’ while outputting a flag signal ‘0’ when it is out of the same area, which means that either of them or both of them amount to ‘0’. Either of those flag signals is supplied to the first and second selection circuits <b>232</b> and <b>236</b> of the color temperature correction circuit <b>23</b> for the purpose of controlling the same selection circuits.

0047The detection circuit <b>17</b> according to the present embodiment detects the video signals having chroma saturation of the maximum set value thereof ST or less as well as luminance of the minimum set value thereof YB or more, which circuit allows not only the signals in pure white, but also those in the white attributes with the slight mixture of other color as well as in the white attributes of lower luminance with the slight mixture of gray. The minimum set value of luminance YB and the maximum set value of chroma saturation ST that are the criteria for detecting the signals in the white attributes are designated by the microcomputer <b>40</b>, which allows the range of the signals in the white attributes as required to be designated in an arbitrary and high precision manner. Further, such sufficiently colored picture area as a human skin, the chroma saturation signal of which area is large in amplitude level and the luminance signal of which area is not of extreme largeness, can be excluded from the detection range of the signals in the white attributes depending on the set values of ST and YB.

0048Then, the color temperature correction circuit <b>23</b> is described below in details with reference to <figref idref="DRAWINGS">FIGS. 7 through 11</figref>. Firstly, a first color temperature correction section <b>231</b> to perform the color temperature correction of the hue signal is described with reference to <figref idref="DRAWINGS">FIGS. 7 through 10</figref>. The first color temperature correction section <b>231</b> is arranged such that it takes a hue indicated with the vector <b>801</b> in <figref idref="DRAWINGS">FIG. 8A</figref> (hue of blue herein) as a reference hue and generates a hue shift coefficient that aggregates to the same reference hue its peripheral hue. <figref idref="DRAWINGS">FIG. 7</figref> shows one example of the circuit arrangement thereof.

0049In <figref idref="DRAWINGS">FIG. 7</figref>, the corrected hue signal as output from the adder <b>202</b> of the hue correction circuit <b>20</b> is input to a hue input terminal <b>2312</b> of the first color temperature correction section <b>231</b>, which corrected hue signal is supplied to one terminal of an adder <b>2322</b>. To the other terminal of the adder <b>2322</b>, the hue offset value (HUEOFFSET) as set by the microcomputer <b>40</b> is input through a hue offset input terminal <b>2311</b>, which hue offset value is also supplied to one terminal of a subtractor <b>2336</b>. The adder <b>2322</b> adds the corrected hue signal to the hue offset value wherein the hue offset value as set by the microcomputer <b>40</b> is equal to the difference T between the digitalized value ‘1024’ and the hue value è of the reference vector <b>801</b> as shown in <figref idref="DRAWINGS">FIG. 8A</figref>, which offset value is found by the following equation, for instance. <br />HUEOFFSET(<i>T</i>)=1024−(353/360)·1024=20

0050Thus, the adder <b>2322</b> outputs the digitalized value ‘0’ as shown in <figref idref="DRAWINGS">FIG. 8B</figref> with a vector <b>802</b>, when a signal having the hue value of the vector <b>801</b> is input thereto. This indicates that the vector <b>801</b> has counterclockwise rotated by the value T to the position of the vector <b>802</b> on the (B−Y) axis. The hue signal that has rotated by the hue offset value as a whole by the adder <b>2322</b> is input to the subtractor <b>2323</b> comprising a first hue shift coefficient generation circuit <b>2340</b>.

0051Hereafter, the operation of the first hue shift coefficient generation circuit <b>2340</b> is described. The subtractor <b>2323</b> outputs a hue signal with 512 subtracted from the hue signal as output from the adder <b>2322</b>. At the same time, the subtractor <b>2323</b> outputs the digitalized value ‘1’ as a code signal when the subtraction turns out to be positive while outputting the digitalized value ‘0’ otherwise. The hue signal as subtracted and output as well as either one of those code signals are input to an absolute value circuit <b>2324</b>, which circuit outputs the input signal as it is when the subtraction turns out to be positive while otherwise subjecting the input signal to the absolute value operation because of it is negative before outputting the same signal. The hue component as subjected to the absolute value operation at the circuit <b>2324</b> is input to a multiplier <b>2325</b> and multiplied by a hue multiplication coefficient as input from the microcomputer <b>40</b> through an input terminal <b>2313</b> so as to be subjected to gain adjustment. The multiplier <b>2325</b> outputs the hue component as subjected to the gain adjustment to the first input terminal of a selection circuit <b>2332</b>. In this way, the first hue shift coefficient generation circuit <b>2340</b> is arranged such that it generates such a hue shift coefficient as rendering the smallest degree of hue shift the hue that is dislocated by 180° from the hue value in the vicinity of blue corresponding to the vector <b>801</b> as shown in FIG. <b>8</b>A and as set by the microcomputer <b>40</b> or by 512 in the terms of the digitalized value and rendering the degree of hue shift greater as the hue gets nearer to the same hue value as dislocated by 180° therefrom. This hue shift coefficient is subjected to the gain adjustment by the multiplier <b>2325</b>. The hue multiplication coefficient for this gain adjustment is adjustable by the microcomputer <b>40</b>.

0052The second hue shift coefficient generation circuit <b>2341</b> outputs a differential signal with the luminance signal Y greater than the minimum set value of luminance YB that is used for detecting the signals in the white attributes in the aforementioned detection circuit <b>17</b>. This generation circuit renders the level of this differential signal null when the luminance signal is smaller than the minimum set value of luminance YB and generates a hue shift coefficient in proportion to the largeness of this differential signal. The gain adjustment for this hue coefficient is also operable by the microcomputer <b>40</b>. Hereafter, the second hue coefficient generation circuit <b>2341</b> is described in details. The luminance signal Y as output from the aforementioned matrix conversion circuit <b>15</b> is supplied through a luminance input terminal <b>2314</b> to a subtractor <b>2326</b>, to the other input terminal <b>2315</b> of which subtractor the minimum set value of luminance YB is supplied. This subtractor subtracts the set value of luminance YB from the luminance signal Y so as to output a differential signal, which differential signal is supplied to a clipping circuit <b>2327</b>, which circuit clips off the negative value of the input luminance differential signal into null so as to output a positive differential signal. The signal as output from this clipping circuit is input to a multiplier <b>2328</b> and is multiplied by the luminance multiplication coefficient as input from the microcomputer <b>40</b> so as to be subjected to the gain adjustment. The multiplier <b>2328</b> outputs the luminance component as subjected to the gain adjustment to the second input terminal of the selection circuit <b>2332</b> as a hue shift coefficient. The straight line <b>1001</b> of <figref idref="DRAWINGS">FIG. 10A</figref> shows the input and output characteristics of the second hue shift coefficient generation circuit <b>2341</b>. It is a luminance multiplication coefficient that adjusts the inclination of the straight line <b>1001</b>. As described above, the second hue shift coefficient generation circuit <b>2341</b> outputs a hue shift coefficient that becomes greater in value as the level of luminance signal becomes greater where the level thereof is at the minimum set value of luminance YB or more. To note, where the level thereof is at the minimum set value of luminance YB or less, the generation circuit outputs the digitalized value of 0 wherein the degree of hue shift is also 0.

0053The third hue shift coefficient generation circuit <b>2342</b> generates a hue shift coefficient on the basis of a differential signal with the chroma saturation signal that is smaller than the maximum set value of chroma saturation ST as used for detecting the signals in the white attributes in the aforementioned detection circuit <b>17</b>. This differential signal amounts to null together with the degree of hue shift when the chroma saturation signal is greater than the maximum set value of chroma saturation ST. Hereafter, the third hue shift coefficient generation circuit <b>2342</b> is described in details. The corrected chroma saturation signal as output from the multiplier <b>221</b> of the aforementioned chroma saturation correction circuit is supplied through a chroma saturation input terminal <b>2318</b> to one input terminal of a subtractor <b>2329</b>, to the other terminal of which subtractor the maximum set value of chroma saturation ST is supplied through an input terminal <b>2317</b>. The subtractor <b>2329</b> subtracts the maximum set value ST from the corrected chroma saturation signal so as to output a differential signal as obtained to a clipping circuit <b>2330</b>, which circuit clips off the negative value of the input differential signal into null so as to output a positive differential signal only. The differential signal as output from the clipping circuit <b>2330</b> is input to a multiplier <b>2331</b>, which multiplier multiplies this differentia signal by a chroma saturation multiplication coefficient as supplied through an input terminal <b>2319</b> from the microcomputer <b>40</b> so as to perform the gain adjustment. The chroma saturation component as subjected to the gain adjustment by the multiplier <b>2331</b> is supplied to a third input terminal of the selection circuit <b>2332</b>. The straight line <b>1002</b> of <figref idref="DRAWINGS">FIG. 10B</figref> shows the input and output characteristics of the third hue shift coefficient generation circuit <b>2342</b>. The inclination of the straight line <b>1002</b> is adjusted by a chroma saturation multiplication coefficient. In this way, where the level of chroma saturation signal is smaller than the maximum set value of chroma saturation ST, the third hue shift coefficient generation circuit <b>2342</b> generates a hue shift coefficient that becomes greater in value as the level thereof becomes smaller. Otherwise, the same circuit outputs the digitalized value of 0 wherein the degree of hue shift also amounts to null.

0054The selection circuit <b>2332</b> selects a signal having either the maximum degree of hue shift or the minimum degree thereof from the signal as input to the first terminal thereof (or as output from the first hue shift coefficient generation circuit <b>2340</b>), that as input to the second terminal thereof (or as output from the second hue shift coefficient generation circuit <b>2341</b>) and that as input to the third terminal thereof (or as output from the third hue shift coefficient generation circuit <b>2342</b> so as to output the same signal. The selection operation thereof by means of the selection circuit <b>2332</b> is controlled in accordance with a switching control signal as input thereto through an input terminal <b>2321</b> from the microcomputer <b>40</b>. In order to facilitate the explanation on the processing of the signal as selected by the selection circuit <b>2332</b>, it is described below with reference to <figref idref="DRAWINGS">FIG. 9</figref> on the assumption that the same circuit selects the signal as input to the first terminal thereof. <figref idref="DRAWINGS">FIG. 9</figref> shows the input and output characteristics of the respective sections of the first color temperature correction section <b>231</b>. <figref idref="DRAWINGS">FIG. 9A</figref> shows the input and output characteristics of an adder <b>2322</b> wherein the hue offset value amounts to null. <figref idref="DRAWINGS">FIG. 9B</figref> shows the input and output characteristics of the first hue shift coefficient generation circuit <b>2340</b> while <figref idref="DRAWINGS">FIG. 9C</figref> showing that of a switching circuit <b>2335</b>.

0055The hue component as output from the multiplier <b>2325</b> is input through the selection circuit <b>2332</b> to a subtractor <b>2333</b> and an adder <b>2334</b>. The hue signal as output from the adder <b>2322</b> is input to the subtractor <b>2323</b> as well as to the subtractor <b>2333</b> and the adder <b>2334</b>. The subtractor <b>2333</b> subtracts the signal as output from the selection circuit <b>2332</b> from the hue signal as output from the adder <b>2322</b>. If the subtraction result turns out to be negative, it is clipped off into null by an integrated clipping circuit, which is not shown in the drawings, so as to be output to an input terminal A of the switching circuit <b>2335</b>. Then, the adder <b>2334</b> adds the hue signal as output from the adder <b>2322</b> to the signal as output from the selection circuit <b>2332</b>. If the addition result turns out to be over 1023, it is clipped off into the maximum value of 1023 by an integrated clipping circuit, which is not shown in the drawings, so as to be output to an input terminal B of the switching circuit <b>2335</b>. When the value of the code signal as output from the subtractor <b>2323</b> amounts to 1 or the subtraction result turns out to be positive, the switching circuit <b>2335</b> selects and outputs the signal as input to the terminal B while amounting to 0 or the subtraction result turns out to be negative, the same circuit selects and outputs the signal as input to the terminal A.

0056That is, the subtractor <b>2333</b> subtracts the signal as shown in <figref idref="DRAWINGS">FIG. 9A</figref> with a waveform <b>901</b> together with that as shown in <figref idref="DRAWINGS">FIG. 9B</figref> with a waveform <b>902</b> during the subtraction period of <figref idref="DRAWINGS">FIG. 9B</figref> or within the output range of the adder <b>2322</b> from 0 to 512 and outputs the subtraction result to the input terminal A of the switching circuit <b>2335</b>. In turn, the adder <b>2334</b> adds the signal as shown in <figref idref="DRAWINGS">FIG. 9A</figref> with a waveform <b>901</b> to that as shown in <figref idref="DRAWINGS">FIG. 9B</figref> with a waveform <b>902</b> during the addition period of <figref idref="DRAWINGS">FIG. 9B</figref> or within the output range of the adder <b>2322</b> from 513 to 1023 and outputs the addition result to the input terminal B of the switching circuit <b>2325</b>. The switching circuit <b>2335</b> switches over to and outputs either one of the signal as input to the terminal A (as output from the subtractor <b>2333</b>) and that as input to the terminal B (as output from the adder <b>2334</b>) according to the code signal as output from the subtractor <b>2323</b>. That is, the same circuit selects the signal as input to the terminal A within the output range of the adder <b>2322</b> from 0 to 512 while selecting that as input to the terminal B within that from 513 to 1023. As the result of it, the switching circuit <b>2335</b> outputs a signal as shown in <figref idref="DRAWINGS">FIG. 9C</figref> with a waveform <b>903</b> wherein the hue has rotationally moved to the direction of 0. The rotational movement of the hue is shown in <figref idref="DRAWINGS">FIGS. 8C and D</figref>. A waveform <b>803</b> of <figref idref="DRAWINGS">FIG. 8C</figref> shows the state where the rotational movement of the hue becomes greater as the hue gets nearer to the (B-Y) axis.

0057The state where the hue rotationally moves is described below with concrete numerical values in use, given that the hue offset value is 0 and the multiplication coefficient to be multiplied by the multiplier <b>2325</b> is 1.

0058Where the corrected hue signal amounts to 10 in value or has a hue closer to blue, the subtractor <b>2323</b> performs the operation of 10−512 and outputs −502 as the result of the operation while outputting 0 as the code signal thereof. The absolute value circuit converts −502 into 502 so as to output the same to the subtractor <b>2333</b> and the adder <b>2334</b>. The subtractor <b>2333</b> performs the operation of 10−502, which results in being negative or −492, so as to output 0 to the terminal A of the selection circuit <b>2335</b>. On the other hand, the adder <b>2334</b> performs the operation of 10+502, which results in being 512, so as to output the same result to the terminal B thereof. The selection circuit <b>2335</b> selects and outputs the signal as input to the terminal A or 0 as the code signal as output from the subtractor <b>2323</b> is 0.

0059Where the corrected hue signal amounts to 600 or has a hue comparatively closer to yellow, the subtractor <b>2323</b> performs the operation of 600−512 and outputs 88 as the result of the operation while outputting 1 as the code signal thereof. The absolute value circuit outputs 88 as it is and supplies the same to the subtractor <b>2333</b> and the adder <b>2334</b>. The subtractor <b>2333</b> performs the operation of 600−88 and outputs 512 as the result of the operation to the terminal A of the selection circuit <b>2335</b>. On the other hand, the adder <b>2334</b> performs the operation of 600+88 and outputs <b>688</b> as the result of the operation to the terminal B thereof. The selection circuit <b>2335</b> selects and outputs the signal as input to the terminal B or 688 as the code signal as output from the subtractor <b>2323</b> is 1.

0060As described above, the present embodiment is arranged such that the color temperature of the hues more distinct from blue increases with the smaller degree of shift so as not to change the hues to great extent while bring arranged such that the hues close to blue have the larger degree of shift so as to come much closer to blue.

0061<figref idref="DRAWINGS">FIG. 8D</figref> shows the rotational movement of the hues as made by a subtractor <b>2336</b>, which subtractor moves rotationally and clockwise by the hue offset value the waveform <b>803</b> as shown in FIG. <b>8</b>C.

0062The first color temperature correction section <b>231</b> is intended for rotationally moving the hue of the color difference signals having a given luminance (the minimum set value of luminance YB) or more and a given chroma saturation (the maximum set value of chroma saturation ST) or less to the direction of blue color for the purpose of increasing the color temperature of the same signals.

0063In the above explanation of the first color temperature correction section <b>231</b>, the case is exemplified where the selection circuit <b>2332</b> selects the signal as output from the first hue shift coefficient generation circuit <b>2340</b>, but it ma be where it selects the signal as output from either the second hue shift coefficient generation circuit <b>2341</b> or the third hue shift coefficient generation circuit <b>2342</b>. It may be also prearranged that the selection circuit <b>2332</b> selects one of the signals as output from the three hue shift coefficient generation circuits in an arbitrary manner wherein the signal as selected by the selection circuit is limited to one kind of them irrespective of the scale and state of the signal as input to the selection circuit <b>2332</b>. Further, the selection circuit <b>2332</b> may be arranged such it selects the signal of the maximum output level among the signals as output from three or two hue shift coefficient generation circuits of arbitrary choice whereas it may be arranged such that it selects the signal of the minimum output level among the signals as output from three or two hue shift coefficient generation circuits of arbitrary choice.

0064Then, one example of the second color temperature correction section <b>235</b> is described in details with reference to <figref idref="DRAWINGS">FIGS. 11 and 12</figref>. The corrected chroma saturation signal as output from the multiplier <b>221</b> of the aforementioned chroma saturation circuit <b>22</b> is input through a chroma saturation terminal <b>2351</b> to one terminal of an adder <b>2356</b>. The chroma saturation differential signal is output from the terminal <b>2320</b> of the first color temperature correction section <b>231</b>, which differential signal is input through a terminal <b>2352</b> to one terminal of a multiplier <b>2355</b>, to the other terminal of which a multiplication coefficient as output from the microcomputer <b>40</b> is input through a terminal <b>2353</b>. The multiplier <b>2355</b> multiplies the chroma saturation differential signal by the multiplication coefficient so as to perform the gain adjustment of the differential signal. The chroma saturation differential signal as subjected to the gain adjustment by the multiplier <b>2355</b> is input to the other terminal of the adder <b>2356</b>, which adder adds the corrected chroma saturation signal to the chroma saturation differential signal as subjected to the gain adjustment so as to output the addition result to a clipping circuit <b>2357</b>. The clipping circuit <b>2357</b>, where the addition result by the adder <b>2356</b> overflows, clips off the same result at a given maximum value. The signal as output from the same circuit is supplied through a chroma saturation coefficient output terminal <b>2354</b> to the other terminal of the switching circuit <b>236</b>. <figref idref="DRAWINGS">FIG. 12</figref> shows the input and output characteristics of the respective sections of the second color temperature correction section <b>235</b>. <figref idref="DRAWINGS">FIG. 12A</figref> shows the same characteristics with a straight line <b>1201</b> when the chroma saturation differential signal amounts to 0 in which no addition is made to the corrected chroma saturation signal at the adder <b>2356</b>. In this case, the second color temperature correction section outputs the corrected chroma saturation signal as output from the chroma saturation terminal <b>2351</b>. <figref idref="DRAWINGS">FIG. 12B</figref> shows the input and output characteristics of the multiplier <b>2355</b> with a straight line <b>1202</b>. As clear from this drawing, the multiplier <b>2355</b> outputs a signal of the maximum level (ST<b>1</b>) when the chroma saturation signal amounts to 0 while outputting a signal of smaller level as the chroma saturation signal gets larger in value. <figref idref="DRAWINGS">FIG. 12C</figref> shows the input and output characteristics of the second color temperature correction section wherein the characteristics thereof is shown therein with a kinked line when the signal as output from the multiplier <b>2355</b> is added to the corrected chroma saturation signal by the adder <b>2356</b>.

0065As described above, the second color temperature correction section <b>235</b> performs the color temperature correction on the chroma saturation signal, which section is intended for increasing the chroma saturation of the signals having a given chroma saturation (the maximum set value of chroma saturation ST) or less so as to make denser in blue the signals in the white attributes whose hue is shifted to the direction of blue color by means of the first color temperature correction section <b>231</b> and to render the pictures on display vividly in white color. This color temperature correction is effective for the case where the chroma saturation level of blue color is originally lower. Such correction for enhancing the chroma saturation thereof is not required for the white color with higher chroma saturation level of blue color (blue enough to be discernible) and/or that intense in warm colors attributes.

0066When the flag signal as output from the detection circuit <b>17</b> corresponds to 1 or where the input signal of high luminance and low chroma saturation is detected, the first selection circuit <b>232</b> selects and outputs the signal as output from the first color temperature correction section <b>231</b>. On the other hand, when the flag signal corresponds to 0 or where the input signal out of high luminance and low chroma saturation is detected, the first selection circuit <b>232</b> selects and outputs the signal as output from the hue correction circuit <b>20</b>. In synchronization with this selection control, when the flag signal corresponds to 1, the second selection circuit <b>236</b> selects and outputs the signal as output from the second color temperature correction section <b>235</b> while selecting and outputting the signal as output from the chroma saturation correction circuit <b>22</b> when the flag signal corresponds to 0. In the above arrangement, the hue signals and the chroma saturation signals are output, which signals are obtained by shifting the hue of only the signals within the range of the color temperature correction (or within the range of those in the white attributes) and by correcting the chroma saturation thereof.

0067The signals as output from the first and second selection circuits <b>232</b> and <b>236</b> are, as described above, converted into the color difference signals by the color difference conversion circuit <b>26</b>, which signals are converted into the three primary colors signals of R, G and B so as to be supplied to the display device <b>28</b>. On the display device <b>28</b>, the pictures as subjected to the color temperature correction in an optimum manner according to the input signals are displayed.

0068In the present embodiment, the color temperature correction is performed on the signals in the white attributes of a given luminance or more and a given chroma saturation or less, which correction is performed on the hue signals and the chroma saturation signals respectively in the digitalized manner so that a more highly precise color temperature correction is realized. Further, the degree to which and the range within which the color temperature is corrected is designated by the microcomputer, which allows such degree and range to be adjusted in an arbitrary manner.

0069<figref idref="DRAWINGS">FIG. 14</figref> is a block diagram to show another embodiment of the present invention, in which the same references are used for the same elements as shown in <figref idref="DRAWINGS">FIG. 1</figref> to avoid redundancy. <figref idref="DRAWINGS">FIG. 15</figref> a view to supplement FIG. <b>14</b>. The difference in <figref idref="DRAWINGS">FIG. 14</figref> with the embodiment as shown in <figref idref="DRAWINGS">FIG. 1</figref> lies in that a hue comparison circuit <b>131</b> is added to the structural elements of the color temperature correction level detection circuit <b>17</b>. The detection circuit with the addition of this hue comparison circuit is referred to as <b>17</b>′, which comparison circuit performs the operation to detect the signals of a given hue among those in the white attributes of a given luminance or more and a given chroma saturation or less so as to exclude the signals of the given hue from the color temperature correction. Hereafter, the arrangement thereof is described below.

0070To one terminal of the hue comparison circuit <b>131</b>, the corrected hue signal as output from the hue correction circuit <b>20</b> is input, to the other terminal of which a hue set value as output from the microcomputer and within the range as shown in hue <b>141</b> of <figref idref="DRAWINGS">FIG. 15</figref>, for instance, is input. This hue set value is intended for designating the range of hue to be excluded from the color temperature correction, which value has two values representing the initial end and the ultimate end thereof. The hue comparison circuit <b>131</b> compares the corrected hue signal with the hue set value and outputs 0 when the corrected hue signal is within those two values while outputting 1 when it is out of those values (or within the range as shown with slanting lines in FIG. <b>15</b>). The switching control circuit <b>173</b>, to which the signals as output from the luminance comparison circuit <b>171</b>, the chroma saturation comparison circuit <b>172</b> and the hue comparison circuit <b>131</b> are input, performs the AND operation of those three signals so as to output a flag signal for controlling the selection circuits <b>232</b> and <b>236</b>. That is, when the luminance comparison circuit <b>171</b> detects a signal of high luminance so as to output 1 and the chroma saturation comparison circuit <b>172</b> detects a chroma saturation signal of low chroma saturation so as to output 1 and the hue comparison circuit <b>131</b> detects a signal out of the hue set values so as to output 1, the switching control circuit <b>173</b> outputs a flag signal corresponding to 1 to the selection circuits <b>232</b> and <b>236</b> so that those circuits select the signals as output from the first and second color temperature correction sections <b>231</b> and <b>235</b>. On the other hand, when the luminance comparison circuit <b>171</b> together with the chroma saturation comparison circuit <b>172</b> output 1 while the hue comparison circuit <b>131</b> detects a signal within the range of the hue set values so as to output 0, the switching control circuit <b>173</b> outputs a flag signal corresponding to 0. Accordingly, because the input signals are out of the range for the color temperature correction, though those signals are of high luminance and an low chroma saturation so as to belong to the white attributes, the selection circuits <b>232</b> and <b>236</b> select the signals as output from the hue correction circuit <b>20</b> and the chroma saturation correction circuit <b>22</b>, which signals are not subjected to the color temperature correction.

0071The present embodiment allows the signals in the white attributes within the range of the designated hue not to be subjected to the color temperature correction. This leads to the restriction of the range of hue on which the color temperature correction is performed, which excludes the signals having a hue that is undesirable to change from the correction of such hue. Further, the range for the color temperature correction is designated by the microcomputer, which range is adjustable in an arbitrary manner.

0072<figref idref="DRAWINGS">FIG. 16</figref> is a block diagram to show another embodiment of the present invention. The difference in <figref idref="DRAWINGS">FIG. 16</figref> with the embodiment as shown in <figref idref="DRAWINGS">FIG. 1</figref> lies in that a luminance correction circuit <b>151</b> is provided therein.

0073In the following description, the same references are used for the same structural elements as shown in <figref idref="DRAWINGS">FIG. 1</figref> to avoid redundancy.

0074The luminance correction circuit <b>151</b> is intended for variably controlling the amplitude and direct current level of the luminance signal as separated from the input picture signals by the matrix conversion circuit <b>15</b>, the detailed view of which circuit is shown in FIG. <b>17</b>. The luminance signal Y as output from the matrix conversion circuit <b>15</b> is supplied to one input terminal of a black expanding circuit <b>1606</b>, to the other terminal of which circuit the maximum set value of black expanding YBK and the gain coefficient as set by the microcomputer <b>40</b> are supplied through an input terminal <b>1602</b>. The black expanding circuit <b>1606</b> variably controls the amplitude of the luminance signal having the maximum set value of black expanding YBK or less so as to output the same signal to one terminal end of a white expanding circuit <b>1607</b>, to the other terminal end of which circuit the minimum set value of white expanding YWT and the gain coefficient as set by the microcomputer <b>40</b> are supplied through an input terminal <b>1603</b>. The white expanding circuit <b>1607</b> variably controls the amplitude of the luminance signal having the minimum set value YWT or more so as to supply the same signal as subjected to the amplitude control to a multiplication circuit <b>1608</b>, which circuit multiplies the same signal by a contrast control coefficient as input through a terminal <b>1604</b> from the microcomputer <b>40</b> so as to variably control the amplitude thereof or subject the same signal to contrast control. A clipping circuit <b>1609</b>, where the signal as output from the multiplication circuit <b>1608</b> overflows, clips off the overflowed portion thereof at the maximum value of 255 in 8 bits precision so as to output the same signal, which signal is input to an addition circuit <b>1610</b>. The addition circuit <b>1610</b> adds the signal as input thereto to a direct current (DC) value as input through a terminal <b>1605</b> from the microcomputer <b>40</b> so as to subject the same signal to brightness control. A clipping circuit <b>1611</b>, where the signal as output from the addition circuit <b>1610</b> overflows, clips off the overflowed portion thereof at the maximum value of 255 in 8 bits precision. The signal as output from the clipping circuit <b>1611</b> is output through a luminance output terminal <b>1614</b> to the inverse matrix conversion circuit <b>27</b>, the detection circuit <b>17</b> and the color temperature correction circuit <b>23</b>. Further, a maximum/minimum level detection circuit <b>1612</b> detects the maximum and minimum level of the luminance signal as input through a terminal <b>1601</b> before the same signal is subjected to the luminance correction and outputs the result to the microcomputer <b>40</b>. The microcomputer <b>40</b> performs the operation of the maximum set value of black expanding YBK and the gain coefficient as input to the black expanding circuit <b>1606</b>, the minimum set value of white expanding YWT and the gain coefficient as input to the white expanding circuit <b>1607</b>, the contrast control coefficient as input to the multiplication circuit <b>1608</b> and the direct current value as input to the addition circuit <b>1610</b> so as to determine the same values.

0075<figref idref="DRAWINGS">FIG. 18</figref> is a view to give the supplemental explanation of the operation of the luminance correction circuit <b>151</b> as mentioned above and shows the input and output characteristics thereof. A waveform <b>1701</b> of <figref idref="DRAWINGS">FIG. 18A</figref> shows the output characteristics of the luminance signal as not subjected to the luminance correction, in which the same signal as input from the terminal <b>1601</b> is output without any correction made thereto. A waveform <b>1702</b> of <figref idref="DRAWINGS">FIG. 18B</figref> shows the output luminance signal, the black and white portions of which signal are expanded by the black and white expanding circuits <b>1606</b> and <b>1607</b>. In the waveform <b>1702</b>, the portion thereof as processed by the black expanding circuit <b>1606</b> corresponds to the continuous line of the set value YBK or less as subjected to the gain adjustment while the portion thereof as processed by the white expanding circuit <b>1607</b> corresponding to the continuous line of the set value YWT or more as subjected to the gain adjustment. A waveform <b>1703</b> of <figref idref="DRAWINGS">FIG. 18C</figref> shows the input luminance signal, which signal is subjected to the contrast control operation by the multiplier <b>1608</b> and the clipping circuit <b>1609</b>. In this drawing, for the facility of understanding, the black and white expanding characteristics thereof are not shown. A waveform <b>1704</b> of FIG. <b>18</b>D shows the output luminance signal where the same signal as shown with the waveform <b>1701</b> is subjected to the brightness control operation by the adder <b>1610</b> and the clipping circuit <b>1611</b>. In this drawing, the black and white expanding as well as the contrast control characteristics thereof are not show for the facility of understanding.

0076As described above, in the present embodiment, not only the luminance control of the luminance signal (or contrast control) and the direct current level control thereof (or brightness control) are performed, but also the gray scale control of the high-level luminance signal (or white expanding control) and that of the low-level luminance signal (or black expanding control) are performed, which allows the luminance signals vivid and rich in gray scale (hereinafter, referred to as corrected luminance signals) to be obtained. Further, the corrected luminance signals are supplied to the detection circuit <b>17</b> and the color temperature correction circuit <b>23</b> at the same time. Thus, the detection of the color temperature correction area (or the area of the signals in the white attributes) at the detection circuit <b>17</b> or <b>17</b>′ with the corrected luminance signals in use correlates with the color temperature correction at the color temperature correction circuit <b>23</b> with the same signals in use. Accordingly, the color temperature correction is optimum also for the display device, the picture quality of which becomes better with the luminance correction.

0077The signal processing circuit including the color temperature correction thereof according to the present invention is described above in details, which processing circuit is used for a direct viewing type or a back projection television receiver as well as for the display or monitoring device of computers. Further, the display device incorporating this signal processing circuit therein is available for not only a cathode ray tube, but also a liquid crystal panel and a plasma display panel (PDP), for instances. Further, according to the kinds of the display devices with the variety of the characteristics such as color reproduction and luminance saturation, it is preferable to alter the parameters such as the minimum set value of luminance YB and the maximum set value of chroma saturation ST relating to the hue and chroma saturation correction, the detection of the area of the signals in white color as well as the color temperature correction by means of the microcomputer <b>40</b> where appropriate, which modification is also included in the scope of the present invention. In any of the above three embodiments, the color temperature correction is performed subsequently to the hue correction and the chroma saturation corrections, the order of which may be reversed. Further, the color temperature correction may be performed without performing the hue and chroma saturation corrections.

0078The present invention allows the hue and chroma saturation of the picture signals of a given range to be corrected in an optimum manner, which allows in particular the color temperature correction of the signals in the white attribute of a given luminance or more and a given chroma saturation or less to be performed with high precision. Further, the color temperature correction is not performed on the signals other than those in the white attributes as designated, which allows the quality deterioration of the pictures having the colors other than the white attribute to abate.